1. Field of the Invention
The invention concerns a helical wind rotor, comprising at least two blades which, as observed in cross section, are of substantially equivalent shape and curved, and are located parallel with the rotational axis and so that the blades are arranged most suitably at equal intervals with respect to the rotation angle of a cylindrical co-ordinate system. In order to bring about helical form of the wind rotor, the blade cross sections are arranged to revolve in the longitudinal direction of the wind rotor.
2. Discussion of Background Art
A conventional rotor of the above presented type, the so called Savonius-rotor, patented e.g. in Finland with number 65940, consists of two blades of the shape of semicircular cylinder, which are located symmetrically with respect to the rotational axis. The cross section of this kind of rotor remains constant along the longitudinal direction and furthermore, the top and bottom edges are provided with cap plates.
In order to further develop the above mentioned rotor, a further reshaped wind rotor is presented in the Finnish patent number 67919. In this so called Windside rotor, the cap plates are removed and a helical form is added, so as to eliminate the so called dead positions in the rotor. In this wind rotor the xy-plane cross section revolves evenly around the wind rotor vertical axis while moving in the longitudinal direction of the wind rotor. The rotor design in question comprises a chassis and two oblong blades with a curved cross section, and which are arranged in the axial direction around the geometrical axis symmetrically, so that the concave blade sides partially overlap each other, leaving an axial gap between the blade inner edges. In addition, the blades are twisted in a helical manner relative to each other. The rotor shaft which is a part of the rotor structure is parallel to the geometrical axis and connected at one end to the chassis. The rotor structure contains, transversally to the rotor shaft, rib-like adapters which connect the blade edges to each other, so as to reinforce the structure. The wind rotor adapters are adjusted successively in the longitudinal direction and additionally, they are domed in cross section, for example in the form of an aircraft wing profile. The concerned publication presents wind rotor applications where the torsion of blades is 180xc2x0.
The above depicted developed wind rotor is especially due to its helical shape distinctly more advantageous than the former comparable ones, because wind from almost any direction causes wind rotor movement. A vital problem related to this type of wind rotor is, nevertheless, the difficulty of its manufacturing which necessitates always making a full wind rotor length mould, because the blades cannot be manufactured by forming of planar sheet blanks. Therefore also the manufacturing costs of the wind rotor type in question are very high, because the manufacturing requires firstly very accurate dimensioning and secondly also high professional skill, in order to arrive at the desired result. Another problem associated with this solution is also that when wind rotors are manufactured with slightly variant dimensioning, entirely individual moulds must be separately dimensioned and manufactured for each.
The helical wind rotor according to this invention is intended to bring about a decisive improvement in the problems described above and thus to essentially enhance the level of technology in this field. To achieve this aim, the wind rotor according to the invention is mainly characterised by that the cross section of the blade belonging to the wind rotor is arranged substantially different from the shape of semicircle, so as to enable manufacturing of the blade of a substantially planar blank.
The most important advantage of the wind rotor according to the invention is facilitating its manufacturing, because it is not necessary to make a concrete full wind rotor length mould, but the desired wind rotor shape can be created even very easily, depending on raw material, for example by mangling planar blade blanks or by bending to the correct shape blade blanks made of elastic material. Using for example thin metal sheets or polymer sheets, the blade may be supported to correct position at only top and bottom edges with for instance a tubular chassis, and the rigid shaft structure keeps the correct height and the rest of the blade settles to correct shape. Accordingly, the blade may also be supported along the helix curves of the inner and outer edges. The manufacturing costs of a wind rotor according to the invention are therefore particularly inexpensive, and also manufacturing of wind rotors of slightly variant dimensioning is easily and accurately feasible, owing to the computational shape definition for the planar blade blanks.
Advantageous embodiments of the wind rotor according to the invention are presented in the related independent claims.
The invention relates also to a method for manufacturing a wind rotor.
The most important advantages of the method according to the invention are its technical simplicity and clarity of the computational preparation or the shape definition for the planar blade blank, which further enables manufacturing of a wind rotor at a very low cost. The vital advantage of the method is that, contrary to prior methods of manufacturing of wind rotors of comparable type, the wind rotor can be dimensioned computationally as unambiguous planar blanks which can be further formed into a very accurately dimensioned wind rotor, using an appropriate method for sheet material forming. The method according to the invention is exceptionally advantageous especially because a full wind rotor length mould is no more necessary, but a wind rotor according to the invention can be assembled using very simple supporting structures, by bending the computationally defined planar blade blank into desired shape. Another vital advantage of the invention is also that the raw material for blades can be chosen more diversely than in prior solutions.